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Abstract

We demonstrate theoretically and experimentally a novel in-fiber Mach-Zehnder interferometer (MZI) with piecewise interference spectrum. The interferometer is constructed by splicing a short section of single eccentric hole-assisted dual-core fiber (SEHADCF) to two single mode fibers (SMFs) with a lateral-offset. Due to the offset splicing and the small distance between cores, different core modes in two cores of the SEHADCF can be excited to form interference at the different wavelength ranges. The discontinuous region of the interference spectrum can be employed as a mark to identify the order of the interference valley. The in-fiber MZI is experimentally investigated as a refractive index sensor, the sensitivity of 353.9 nm/RIU is obtained in the RI range of 1.335 ~1.395. The in-fiber MZI with a high sensitivity has a great potential in biological and chemical applications. Especially, due to the ability to identify the order of interference valleys by the discontinuous region, the proposed in-fiber MZI can improve the reliability of fiber sensors in remote monitoring applications.

Fig. 2 The dispersion curves for different modes and typical field distributions in the SEHADCF. (a) The effective RI of modes in the SEHADCF at different wavelengths. (b) - (i) Field distributions of different modes in the SEHADCF. (b) and (c) LP01 and LP11 modes of the center core at 980 nm. (d) and (e) LP01 and LP11 modes of the suspended core at 980 nm. (f) LP21 mode at 940 nm. (g) and (h) LP01 mode of the center and suspended cores at 1310 nm. (i) LP11 mode of the suspended core at 1310 nm.

Fig. 4 Transmission spectra of SEHADCF-based MZI. (a) The transmission spectrum of SEHADCF-based MZI in the wavelength range from 600 to 1600 nm. The light source is an ultra-continuous spectrum fiber laser (SC-5, Yangtze Soton Laser Co., Ltd.), and the OSA is AQ6370C (YOKOGAWA Inc.). The bottom-left inset is the micrograph of the splicing point between the SMF and the SEHADCF. (b) The transmission spectrum of SEHADCF-based MZI with the wavelength range from 1200 to 2400 nm. The light source is an ultra-continuous spectrum fiber laser (SuperK Compact, NKT Photonics Inc.), and the OSA is AQ6375B (YOKOGAWA Inc.).

Fig. 5 The RI response of the sensor. (a) The transmission spectra of the sensor injected solutions with different RIs. (b) and (c) are partial zoomed views of the transmission spectra in the wavelength range from 1415 to 1455 nm and from 1495 to 1530 nm, respectively. (d) and (e) are the relationships between wavelengths of the 5th and the 13th interference valley and RI, respectively. Inset: the field distribution of the excited high-order cladding mode by simulating calculation.